1. Field of the Invention
The present invention relates to a sheet feeding apparatus in an image forming apparatus such as a copying machine, printer and others, and particularly to a feeding apparatus of a vacuum type.
2. Description of Related Art
An apparatus shown in FIGS. 5 and 6 has been known as a typical example of such sheet feeding apparatuses.
The illustrated apparatus comprises a frame 94 having air suction apertures 92 communicated with a vacuum plenum 91 and provided at its lower surface with a projected guide member 93, suction belts 97 having a large number of air suction apertures and retained around drive and driven pulleys 95 and 96 to be moved along the frame, a tray 98 disposed below the belt for supporting sheets to be fed, and a retainer member 99 disposed downward, in a sheet feeding direction, the tray for blocking advance of the sheets lower than the top sheet.
According to this apparatus, the sheets P laid on the tray 98 are sucked in sequence from the top by the suction belts 97, and are fed to an image forming section by the feeding movement of the belts in a direction indicated by an arrow f in the Figure. The lower sheet P2 which tends to be sucked and fed together with the top sheet P1 is prevented from advancing by the retainer member 99, as shown in FIG. 6.
In the prior art apparatus, the suction belts 97 extending along the frame 94 are disposed at both sides of the projected guide member 93 provided at the lower surface of the frame, so that the belts 97 relatively rapidly suck the outer portions of the top sheet P1 faced to the belts 97. The sheet P1 will not bend any longer along the guide member 93 due to the friction force between the sheet and the belt 97, so that large spaces A and B formed adjacent to the guide member 93 will be maintained. This reduces a gap between the top sheet P1 and the lower sheet P2. Therefore, the retainer member 99 cannot reliably block the advance of the lower sheet P2, which frequently causes double feeding of the sheets.